The role of swash infiltration in determining the beachface gradient: a numerical study

✍ Scribed by Gerhard Masselink; Ling Li

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 293 KB
• Volume: 176
• Category: Article
• ISSN: 0025-3227
• DOI: 10.1016/s0025-3227(01)00161-x

✦ Synopsis

On sand and gravel beaches, the increase of the gradient of the beachface with increasing sediment size has been attributed to swash in®ltration. The present study uses a process-based numerical model to examine in detail the role of swash in®ltration in determining the beachface gradient. It is found that swash in®ltration increases the onshore asymmetry in the swash ¯ow, thereby enhancing onshore sediment transport and resulting in relatively steep beachface gradients. However, the accretionary effects of swash in®ltration are only evident when the rate of in®ltration is suf®ciently large, i.e. when the total in®ltration volume over a wave cycle exceeds c. 2% of the uprush volume. This threshold is attained when the hydraulic conductivity exceeds 1 cm/s which is approximately equivalent to a grain size coarser than 1.5 mm. This ®nding suggests that the correlation between beachface gradient and sediment size observed on sandy beaches is not due to enhanced swash asymmetry caused by swash in®ltration. For gravel beaches, however, swash in®ltration is likely to be the dominant factor in controlling the beachface gradient with increased hydraulic conductivity (i.e. sediment size) resulting in steeper beachface gradients.